Make xperf output decoding more robust

When running IdentifyChromeProcesses.py on a customer trace I hit
decode exceptions due to non-ASCII characters. Setting the encoding to
utf-8 did not resolve them so I also added errors='ignore' because I
want this script to always run to completion and give best-effort
results.

The error messages seen in UIforETW looked like this:

Traceback (most recent call last):
  File "C:\Users\brucedawson\Desktop\etwpackage\bin\IdentifyChromeProcesses.py", line 353, in <module>
    main()
  File "C:\Users\brucedawson\Desktop\etwpackage\bin\IdentifyChromeProcesses.py", line 350, in main
    _IdentifyChromeProcesses(args.trace[0], args.cpuusage, args.tabbed, False)
  File "C:\Users\brucedawson\Desktop\etwpackage\bin\IdentifyChromeProcesses.py", line 130, in _IdentifyChromeProcesses
    line = line.decode()
UnicodeDecodeError: 'ascii' codec can't decode byte 0xe3 in position 261: ordinal not in range(128)

bin/IdentifyChromeProcesses.py

@@ -127,7 +127,7 @@ def _IdentifyChromeProcesses(tracename, show_cpu_usage, tabbed_output, return_pi
 
   for line in output.splitlines():
     # Python 3 needs the line translated from bytes to str.
-    line = line.decode()
+    line = line.decode(encoding='utf-8', errors='ignore')
     # Split the commandline from the .csv data and then extract the exePath.
     # It may or may not be quoted, and may or not have the .exe suffix.
     parts = line.split(', ')